The present invention relates generally to improved mobile communications and, more specifically, to a new mobile unit cradle including an antenna and heat sink combination for portable cellular phone vehicle kits.
With the proliferation of mobile communications, cellular phone operation has become commonplace in daily life. One prominent area of use for cellular phone technology is in connection with motor vehicles. As shown in FIG. 1, mobile communication is established through networks of base stations 20 which are set up to communicate with mobile units or stations in vehicles 10 such as cars. Today many vehicles include mobile phone kits. As shown in FIG. 2, these kits typically have a cradle 25 for a portable phone 27 and also include a hands-free unit 30 having a microphone 32 and a speaker 35 to allow a driver or passenger to communicate without having to pick up the portable phone 27.
It is well known today that the signal quality associated with the unaided use of portable phones inside an automobile or other vehicle will be severely degraded by the radio frequency (RF) shielding effect of the vehicle's metal body. Typically a vehiche's body can account for as much as 10 dB of RF attenuation when trying to use a portable phone inside a vehicle. In order to avoid this 10 dB vehicle shielding loss, an external antenna 40, also shown in FIG. 2, is commonly used. The portable phone 27 has an external antenna port (not shown) which allows its transmission circuitry to be connected to the cradle 25. The cradle 25 in turn is connected by cabling 50 to the external antenna 40. The external antenna 40 can, for example, be fabricated as a halfwave dipole with 3 dB of gain, and is attached to the outside body of the vehicle 55. The additional 3 dB gain associated with the external antenna is used to overcome a 3 dB loss generally associated with the RF cabling, connectors, and isolation devices between the portable phone 27 and the external antenna 40. Alternatively, an RF booster 60 may be used to overcome losses introduced by these elements.
Present methods for electrically connecting the portable phone to the external antenna take several approaches. One approach is the direct connection described above between the portable phone's external antenna port and an external antenna connector of the cradle unit. Capacitive or inductive coupling of the portable phone's antenna to the cradle antenna can also be used. However, each of these techniques for coupling the portable phone to the external antenna suffers from the dual drawbacks that the portable phone must be physically compatible with the cradle and that the portable phone must be physically positioned within the cradle to obtain the benefits associated with connection to the external antenna. Thus users are restricted in the manner in which they can use their portable phones within vehicles.
In other conventional vehicle kits, the cradle is omitted. For example, a portable phone's antenna can be used to transmit to, and receive RF signals from, a separate "in the vehicle" antenna which is directly, capacitively, or inductively connected to the external antenna on the opposite side of the wall 55 of the vehicle body as the external antenna 40. This technique also avoids the 10 dB vehicle body loss. However, in this configuration, the other benefits of the cradle are lost, such as the hands-free unit and battery charging circuitry for replenishing the portable phone's battery.
As mentioned above, vehicle kits also typically include hands-free units connected to the cradle 25. These kits provide hands-free operation through use of an external microphone 32 and speaker 35. Vehicle kits also typically include circuitry for recharging the portable phone's battery when the portable phone 27 is placed in the cradle 25. Some cradles are also provided with an RF transmitter booster and a low noise receiver that can be switched into the transmit/receive path between the portable phone 27 and the external antenna 40. However, these various circuits may generate a great deal of heat which in turn may impact the performance and lifetime of the cradle.